Propeller



Feb. 19, R953 A. s. MULLGARDT PROPELLER 4 Sheets-Sheet 1 Filed April 30, 1945 INVEN TOR. ALEXANDER 5T Nous/mp7 BY 2 Feb. 10, 1953 A. s. MULLGARDT PROPELLER 4 Sheets-Sheet 2 Filed April 50, 1945 IN VEN TOR. ALEXANDER 5. MULLQARDT BY Feb. 10, 1953 A. s. MULLGARDT 27,

PROPELLER Filed April 50, 1945 4 Sheets-Sheet 3 INVEN TOR. ALEXA NDEE 5. Muuqmzpr Feb. 10, 1953 A. s. MULLGARDT 2,627,928

PROPELLER Filed April 30, 1945 4 Sheets-Sheet 4 IN VEN TOR. A LEXA NDER 5 MUL L qA EDT Patented Feb. 10, 1953 UNITED STATES PATENT OFFICE 1 Claim.

This invention relates to propellers whose average pitch as well as whose geometric pitch is adjustable at an time.

The various features of the herein invention can be utilized in connection with propellers used for propulsion as on airplanes, or, for fixed installations of air moving equipment, or for controlled vertical rise, hovering, and translational flight as on helicopters or helicoplanes, or for controlled autorotative sustaining surfaces as on autogiros; further the various features of the invention are applicable to propellers with rigid blades or propellers with articulated blades, whether the blades are articulated around one axis or several axes.

An object of the invention is to provide a propeller with blades, the geometrical pitch of which is adjustable in such a manner that the reduc-' tion of the elficiency under varying operating conditions, which otherwise results in propellers whose combined average pitch and geometric pitch is not adjustable, is minimized. In other words, the amount of twist from root to tip of the blades as well as the amount of pitch of the blades, is adjustable at any time so as to approximate closely the optimum efliciency for various imposed operating conditions.

Another feature of the invention is to provide a propeller, the blades of which are made of relatively adjustable blade elements and. to provide connection between the blade elements and a mechanism for adjusting the relative adjustment of the blade elements to obtain a desired geometric pitch.

Another object of the invention is to provide a propeller with blades of adjustable geometric pitch. and to provide a mechanism which will vary the geometric pitch of the propeller blades individually throughout each revolution of the propeller so as to substantially compensate for cyclic variations of the relative wind, or to induce varying thrust distribution at desired points in the cycle of revolution; by such cyclic adjustment, a higher overall efficiency of operation is achieved, control of the aircraft is obtained, vibration of the propeller or rotor due to oscillation of its blades about their respective hinged axes or due to deflection of its blades away from a normal radial position is reduced to a minimum; and undue strains and stresses on the aircraft are obviated.

I am aware that some changes may be made in the general arrangements and combinations of the several devices and parts, as well as in the details of the construction thereof without departing from the scope of the present invention as set forth in the following specification, and as defined in the following claim; hence I do not limitmy invention to the exact arrangements and combinations of the said device and parts as described in the said specification, nor do I confine myself'to the exact details of the construction of the said parts as illustrated in the accompanying drawings.

With the foregoing and other objects in view, which will be made manifest in the following detailed description, reference is had to the accompanying drawings for the illustrative embodiment of the invention, wherein:

Fig. 1 is a diagrammatic side view of a propel ler, the inflow windbeing substantially parallel to the axis of rotation of the propeller. I,

Fig. 2 is a diagrammatic plan view of a propeller showing the chordwise components of said relative wind in the disc of rotation.

Fig. 3 is a diagram showing the components of the relative wind on a blade element.

Fig. 4 is a diagrammatic side view of a propeller with the inflow wind at an angle to the propeller axis.

Fig. 5 is a plan view of the propeller showing the chordwise components of said inclined relative wind in the disc of rotation.

Fig. 6 is a sectional view of a propeller blade and its mounting, the propeller blade being made of a pair of blade elements.

Fig. 7 is a sectional view, the section being taken on lines 1'! of Fig. 6.

Fig. 8 is a sectional view, the section being taken on lines 88 of Fig 6.

Fig. 9 is a sectional view, the section being taken on lines 99 of Fig.6.

Fig. 10 is a plan view partly broken away of a blade with two floating blade elements between the root element and tip element.

Fig. 11 is a sectional view taken on lines I Il l of Fig. 10.

Fig. 12 is a sectional view taken on lines 12-42 of Fig. 10.

Fig. 13 is a sectional view, the section being taken on lines l3--l3 of Fig. 10.

Fig. '14 is a sectional view, the section being taken on line I 4-14 of Fig. 10.

Fig. 15 is a partly sectional and fragmental view of a blade of my construction with several floating blade elements between the root element and tip element.

In connection with the usual type of propellers, the blade of the propeller may be considered to be torsionally rigid about its radial axis from root to tip and any change in the complete blade setting with respect to the disc of rotation will impose a varying degree of efiectiveness of the blade elements located at progressive points along the radius. Usually a blade in the past has been designed so that under one particular set of conditions involving required thrust, rotational speed, velocity of incoming air, and direction of that air, it will give a certain peak efliciency with respect to the power input from the motor. This condition is illustrated in Figs. 1 and 2, wherein I show a graphic illustration of a propeller I under uniform and constant inflow velocity with the direction of wind parallel to the axis of rotation as indicated by arrows 2. Under these conditions, the propeller rotating at uniform and constant velocity of revolution in the disc of rotation indicated by the broken line circle 3 in Fig. 2 and in the direction of the arrow 4, the vectors 6 represent substantial air velocity impinging on blades and due to rotation only.

In any propeller it is essential to appreciate that for ideal efficiency, each blade and every element in each blade must be contributing equally to the required thrust. At fair approximation of ideal blade loading may be achieved provided the propeller is so designed that the blade elements of the blade work substantially equally from a point as close to the axis of rotation as practicable. Every propeller must be considered in the light of two separate and distinct velocities, namely the velocity of the various blade elements in their plane of rotation and the air velocity passing through the disc. This is represented by a simple vectorial diagram in Fig. 3, wherein a blade element of the propeller l is shown in relation to the two contributing velocities at right angles to one another. The horizontal arrow line 1 represents the velocity of the blade element parallel with the disc of rotation of the blades indicated by the line 8. The vertical line 9- represents the velocity of inflow. It is to be noted that the blade in Fig. 3 is set for zero lift. The vertical broken line ll indicates the axis of the rotation of the propeller in Fig. 3. Under these conditions the resultant velocity indicated by the line '2 in Fig. 3 will give the magnitude and direction of the airflow which must meet the element of the blade. This resultant will vary in magnitude and direction for each blade element from tip to the innermost element because of the elements changing speed in the disc of rotation;

when a blade is designed to anticipate these ra-- dially varying directions of air, the innermost blade element is set at a much greater angular setting than the element at the tip. Such angular settings ideally should be such as to give to each blade element a setting where it will offer the least resistance to the resultant air for the required thrust. This angularly differential set ting of the blade element from the root to the tip of the blade, is usually called the basic geometric pitch, and is expressed in distance per revolution of the relative movement between the air and the propeller.

In Figs. 4 and 5 I show graphic illustrations of the propeller l where the uniform and constant inflow velocity as indicated by the arrows I3 is not parallel tothe axis of rotation. As particularly indicated in Fig. 5, the component representing the air velocity which lies in the propeller disc of rotation must be added to or subtracted from the blade element rotational speed, at each increment of radius of the blade. It will become additive when the air velocity opposes the rotational velocity, and subtractive when the rotational velocity and the disc component of the air velocity are in the same direction. The vectors or arrows M in Fig. 5 represent air velocity due to rotation only. The other vectors I6 represent size and direction of the horizontal component of the inflow air velocity impinging on the blades at blade azimuth positions B and C respectively where they are maximum. This is a chordwise component on the blade. As the diagram in Fig. 5 shows, this chordwise component has decreased to zero at blades azimuth position A and A, and varies as the sine of the azimuth angle 1// measured from the down wind position of each blade respectively on its cycle of revolution. The graphic illustration in Fig. 5 is substantially to illustrate the true condition which exists with respect to the chordwise components when the direction of inflow wind is not parallel with the axis of rotation, and to illustrate that except for two instantaneous positions during a cycle of revolution, the geometric pitch of each blade should be changed at each instant. A mean condition from which to determine the basic geometric pitch occurs only when a blade is pointing either into or away from the relative wind direction, because then the chordwise component of the inflow wind is zero.

With a blade at position C in Fig. 5, the point I! is a point of zero net, or efiective, chordwise velocity in the disc; toward the blade-root the net chordwise air direction is reversed. Therefore, the space or distance X is a measure of the minimum range of positive chordwise velocities in the disc, and the space or distance Y is a measure of the maximum range of negative chordwise velocities in the disc; that is, when a blade is at any other cycle position than at C. a greater percentage of the blade span is operating in the range of positive chordwise velocities in the disc. This particular condition exists especially in connection with helicopters or autogyros, or helicoplanes and the like where the inflow wind direction is often much closer to being parallel with the propeller disc than with the axis of rotation and correspondingly the variations in geometric pitch per revolution should be made much greater for optimum efficiencies.

In adjustable pitch propellers heretofore used, adjustment is made in the effort to adapt to the varying conditions of operation by the turning of the entire blade; that is all the blade elements turn as a rigid unit. Each such blade however, is designed to operate with the greatest efflciency at one given condition of flight of the aircraft or at one given condition of performance in any other device where such propellers may be used. When there is a change or departure from the condition for which the geometric pitch of the blade was designed then there is a very substantial decrease in the efiiciency of the propeller. Adjustments heretofore used, namely the turning of the rigid blades endeavored to reduce slightly this loss of efiiciency at varying conditions, but the loss still remains great. In my invention the basic geometric pitch of the blade is varied progressively within extreme limits so as to compensate for the variation of conditions, and to provide a propeller which will minimize decrease of efficiency of the propeller operation under varying conditions or on the variation of the direction of the inflow wind. L1 connection with propellers of the type which are subject to cyclic changes of relative wind, I additionally adjust the geometric pitch of the blade to compensate for such cyclic changes. In this manner high efficiency of the propeller is accomplished not only on one given condition of operation, but also under varying conditions within predetermined extreme limits.

In carrying out my invention, in the embodiment shown in Figs. 6 to 9 inclusive, I make use of a spar I 8 which is journaled in a suitable sparroot journal E9 in a hub extension 2| of a hub not shown. The hub extension 2| may be mounted on a propeller hub rigidly or it may be articulated in any suitable manner. The number of hub extensions 2| depends upon the number of blades on a propeller. Each blade in a propeller being of the same structure as the others, the showing of one blade and its description will sunice and apply to the other blades of the propeller. The blade in this illustration is shown as made of a root element 22 and a tip element 23. Each element is constructed in any suitable manner, for instance with ribs 24 shaped as shown in Figs. 8 and 9 and covered with the usual skin 23. The ribs 24 of the root element 22 are mounted on a sleeve 2'! which sleeve in turn is journaled at 28 on the spar [8. A collar 29 on the spar l3 resists the centrifugal thrust. The tip element 23 is secured by suitable pins or the like at 3| to the outer portion of the spar I8. The adjacent ends of the root element 22 and the tip element 23 have ribs 32 which are respectively divergent to each other both toward the leading edge 33 and toward the trailing edge 34 of the blade. The spacing between the adjacent ribs 32 of the root element 22 and of the tip element 23 is covered with suitable elastic skin 35, so as to provide for continuous blade surface and continuous leading and trailing edges at any relative adjustment of the root element and tip element at various geometric pitch.

The adjustment of the geometric pitch of this blade is accomplished by suitably turning the root element 22 and the tip element 23 in their respective directions and to a desired degree for the selected geometric pitch. For accomplishing this adjustment I show in this illustration a spar lever 37! suitably keyed or secured to the spar and a sleeve lever 38 connected to the sleeve 21. By suitable adjusting mechanism, illustrative embodiments of which are hereinafter described, these levers 3'1 and 38 are turned so as to respectively turn th spar l3 and the sleeve 21 and the element 22 and the tip element 23 therewith, to the relative adjustments required fora desired geometric pitch. For additional control of the adjustment, a yieldable and resilient resistance is introduced between the relatively adjustable blade elements. In the present illustration this is shown in the form of a leaf spring 39, one end 4| of which is attached to the rib 32 of the root element 22 at the trailing edge 34 of the blade. The other end 42 of the leaf spring 39 is slidably held in a slot 43 in the inner rib 32 ofthe tip element 23 so as to allow for the elongation or shortening of the trailing edge according the relative adjustment of the blade elements to the selected geometric pitch. If the blade elements are turned relatively to one another this turning movement is resiliently resisted by the leaf spring 33.

Another embodiment of my invention is shown in Fi s. to 14 inclusive, in which is shown a propeller blade with a larger number of segments or blade elements and with an irregular plan-form. This embodiment also includes a spar 44 journaled in a hub in the manner heretofore described. On this spar 44 is journaled a root element 46 in the manner shown in detail and described in Fig. 6. A tip element 41 is spaced radially from the root element 45 and is secured to the outer end of the spar 44. In the space between the root element 46 and the tip element 41 are two transverse floating blade elements 48. All the blade elements are adjustable about the axis of the spar 44 and are substantially at right angles to said axis. Each floating element 48 is journaled by sleeves 49 on the spar 44. The adjacent ribs 5| of the adjacent blade elements diverge toward the respective edges of the blade so as to provide a space for the elongation or shortening of said edges according to the respective adjustments of the selected geometric pitch. The space between the end ribs 5| of the adjacent blade elements are covered with elastic skin 52 so as to provide continuous blade surface and blade edges at the various adjusted geometric pitch. Yieldable resilient resistance is introduced between the adjacent blade elements, and for the purpose of illustration this resistance is again shown in the form of leaf springs 53 connected to the end ribs respectively in the same manner as leaf spring 39 in the form described in connection with Fig. 6.

A spar lever 31 is connected to the spar 44. A

sleeve lever 38 is connected to the sleeve of the root element 43. The intermediate blade elements 48 are floating about the axis of the spar 44 so as to conform to the contour as determined by the relative adjustments of the rootelement 46 and the tip element 4?. Thus by turning the levers 31 and 33 by suitable adjusting mechanism, the root element 46 is turned to a given or selected angle about the axis of the spar 44, and the tip element 41 is turned to a different angle as may be required for the desirable geometric pitch. The elastic skin 52 and the leaf spring 53 move the intermediate floating segments or blade elements 48 about the same axis and to such angles of adjustment as to form a continuous blade surface and blade edges conforming to said geometric pitch determined by the relative adjustment of the root element 43 and the tip element 4?. Fig. 11 shows the angular adjustment of the root element 43. Fig. 14 shows the adjustment of the tip element 4?. Figs. 12 and 13 show the corresponding angular adjustment or displacement of the floatin elements 48 as determined by the relative positions of the root and the tip elements and as additionally determined in this instance by the restraint imposed by the connecting elastic skin 52 and springs 53. In a certain geometric pitch adjustment of the blade the relative angles of the four blade elements of this form would appear in sections as shown in Figs. 11 to 14.

The embodiment of the invention shown in Fig. 15 is a multisegment blade with any desired large number of floating blade elements 54 between the root element 53 and the tip element 5 The root element is mounted on a sleeve 58 which in turn is journaled on the spar 44. The tip element 51 is flxed to the outer end of the spar 44. The inner end of the spar 44 is journaled in a hub as heretofore described. In this instance there is a continuous elastic skin coverin from the tip element to the root element. At the leading edge of the blade reinforcing links 59 are provided which fit into suitable slots on the ribs of all adjoin in blade elements or segments. The outer surfaces of the blade are contoured to suitable airfoil section to give support to the elastic skin over the'high pressure regions. In this form, as in the previous forms, a yieldable resistance may be introduced in addition to the elastic skin, and is illustrated herein in the form of leaf springs 51 connected to adjoinin blade elements in the manner heretofore described. A spar lever 31 is connected to the spar 44. and a sleeve lever 38 is connected to the sleeve 58 of the root element 56 for the relative adjustment of said root element 56 and the tip element 51 of the blade, respectively. The intermediate floating blade elements 54. will assume angular positions as determined by the relative positions of the root element 56 and the tip element 51 and by the degree of restraint imposed by the elastic skin. This form is particularly suitable for extreme range of operating conditions, such as those expected when a propeller progressively passes through autorotative, helicopter, or helicoplane, states with either coaxial or off-axial airflow.

I claim:

A propeller blade including a root segment, a tip segment, and a plurality of intermediate segments, a spar coaxial to all of said segments, a device to select the relative pitches of said se ments about said spar, flexible covering connecting said segments to conform to the amount of spiral twist of said blade according to the rela- 8 tive adjustments of the root segment and the tip segment, and resiliently yieldable means at said flexible cover connections engaging the adjacent segments to yieldably determine the relative pivotal movements of said intermediate segments.

- ALEXANDER S. MULLGARDT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,449,129 Pescara Mar. 20, 1923 1,526,230 Pescara Feb. 10, 1925 1,919,089 Breguet July 18, 1933 1,986,709 Breguet Jan. 1, 1935 2,108,417 Stanley Feb. 15, 1938 2,162,794 Asboth June. 20, 1939 2,308,802 Bariing Jan. 19, 1943 2,329,133 Peed Sept. 7, 1943 2,475,121 Avery July 5, 1949 FOREIGN PATENTS Number Country Date 752,142 France Sept. 1-6, 1933 851,766 France Jan. 15, 1940 

